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G'day Zule,
OK, I have had a bit of a scrounge for info about AC traction motor control.
The phrase Electrical Cabinet, or Electrical Locker can be used to describe where the majority of the electrical control equipment is located.
Depending upon the locomotive manufacture and model, there can be from one to three electrical cabinets utilized.
Numerous electronic components are located inside the electrical cabinet.
Including; Traction Rectifiers, Control Rectifier, Transformers, Contactors, Relays, Computer modules, Switches etc.
The DC traction electrical cabinet found on DC locomotives also contains much of this equipment, but not that associated with AC Traction.
Two Traction Control Converters are another important facet of AC traction control.
One Traction Control Converter for each bogie, thereby for two or three traction motors, depending upon wheel arrangement.
The Traction Control Converters house the Traction Inverters which convert the DC current into variable frequency 3 phase current.
The Inverters are controlled by the primary control computer which is connected to the drivers control stand.
Inside the Electrical Cabinet, AC current produced by the AC Alternator connected to the engine is converted into DC by the Traction Rectifiers.
This DC current is linked to the Traction Inverters to become the controlled variable frequency 3 phase current going to the traction motors.
Gate Pulse via either Thyristors or Bipolar Transistors is utilized to create the variable frequency of the output current.
A controlled voltage of from 0 VAC up to 2000 V 3 phase AC can be created with a maximum of 1200 Amps AC.
AC traction motors are generally lighter in weight compared to a comparable DC traction motor.
There are NO Short Time Ratings working in maximum traction motor amps as there applies to DC traction.
Increased adhesion is possible with AC traction due to the ability to remain at high power low speed.
An average 3000 hp DC traction locomotive may achieve between 28% - 31% adhesion.
Whereas, an AC traction locomotive may achieve between 35% - 40% adhesion.
This increase in adhesion permits working comparable load trains with fewer locomotives.
There are a lot more electronics associated with AC traction.
AC motors are more difficult to control.
Another difference may be the lack of an oil float governor on the engine of a modern AC traction locomotive.
The engine control being fully digital with electronic fuel injectors etc.
But, loose the primary computer system, and your locomotive becomes a failure.
I guess that you need to be an electrical engineer to understand all of the facets involved.
I am certainly not capable of the technical details, but I kinda understand the basics.
Steve.
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